Generally, bicycles are moved forwards in such a way as to rotate wheels using the force generated when a user pushes the pedals. In a wide meaning, the word bicycles include three or four-wheeled bicycles and bicycles, such as water bicycles, ice bicycles, etc., which are used on places other than the ground. The bicycles have been widely used as a representative means of transportation which is operated by manual force. In particular, recently, bicycles are used in various manners, for example, as exercise devices for improving the health or as a means for recreation. Furthermore, the demand for bicycles has increased due to their environment-friendly characteristics.
Typically, such a bicycle includes wheels, a frame, pedals, a chain, a saddle and a handlebar. Most bicycles have a saddle height adjustment unit which is provided on the junction between the saddle and the frame. Thus, to ensure the stability of a user who sits on the saddle, the height of the saddle can be adjusted depending on the height of the user such that his/her feet can be appropriately put on the pedals.
As such, in the case of conventional bicycles, the saddle can be adjusted in height such that the distance between the feet of the user and the pedals can be adjusted. However, users have a variety of body types. Even though the users have the same height and leg length, the lengths of the upper bodies or arms differ from each other. That is, in the case where the legs of the user are longer than the average for humans of the same arm length, even if the height of the saddle is set suitable for the length of the legs of the user, the user may not easily hold the handlebar. Conversely, if the legs of the user are relatively short, because the arms must be bent when the user holds the handlebar, it is very uncomfortable, particularly, when riding the bicycle for a long time. Furthermore, the above problems are further aggravated because the user cannot adjust the angle of the saddle while the bicycle is moving.
In addition, when the bicycle is going up or down a slope, the user is inclined forwards or rearwards with respect to the bicycle. In the case where the angle of the saddle is fixed, because it is uncomfortable to sit on the saddle, generally, the user stands up. However, as such, when the user stands up, because his/her weight is applied only to the pedals, the stability is deteriorated and the probability of an accident increases. Moreover, if the bicycle goes up or down the slope for a long time, because the user must maintain the standing up position for that time, the fatigue of the user is increased.
As described above, in the conventional techniques, the angle of the saddle cannot be adjusted when the bicycle is moving. Therefore, if the user is uncomfortable when riding the bicycle, he/she must stop the bicycle and get off to adjust the angle of the saddle, which is inconvenient for the user.